Amylin shares rose 48 percent to $22.72 at Noon Eastern time today after Bloomberg News said Bristol privately bid $3.5 billion, or $22 a share, to acquire Amylin. The report was based on two people knowledgeable about the unsolicited offer. Official spokespeople for both companies declined to comment to the news service.

Amylin has endured some rough times of late, most recently because of a troubled alliance with Eli Lilly and a string of regulatory delays for its diabetes drug exenatide (Bydureon). But Amylin’s prospects have significantly improved in recent months. In November, it terminated its collaboration with Lilly, and two months later it won FDA clearance to start selling Bydureon as the first diabetes drug that can be injected as little as once a week. Amylin is facing competition from Novo Nordisk’s liraglutide (Victoza), but escaping the Lilly deal has given it new flexibility to pursue a new marketing partner to help pitch exenatide (Byetta) and the longer-lasting version (Bydureon) around the world.

Tom Russo, an analyst with Robert W. Baird, said today in a note to clients he has forecasted that Bydureon could generate $1.5 billion in sales in 2017, which he said makes Amylin worth $19 a share.

Surely some of today’s stock action is driven by speculation that all this talk of Amylin finding a new marketing partner will end up culminating in some other takeover bid. Bristol-Myers has already made one significant acquisition in the past year, with its $2.5 billion deal to buy Alpharetta, GA-based Inhibitex (NASDAQ: INHX), the developer of drugs for hepatitis C.